An amputee is a person who has lost part of an extremity or limb such as a leg or arm, the remainder of which commonly may be termed as a residual limb. Residual limbs come in various sizes and shapes with respect to the stump. That is, most new amputations are either slightly bulbous or cylindrical in shape while older amputations that may have had a lot of atrophy are generally more conical in shape. Residual limbs may further be characterized by their various individual problems or configurations including the volume and shape of a stump and possible scar, skin graft, bony prominence, uneven limb volume, neuroma, pain, edema or soft tissue configurations.
An artificial limb was designed to replace the portion of the limb lost through the amputation. One example of an artificial lower limb is shown in FIG. 1. Limb 100 includes socket 102, into which residual limb 110 is inserted, shin portion 104 and foot 106. Historically, artificial limbs typically used by a leg amputee were, for the most part, all made out of wood, such as an Upland Willow. The limbs were hand carved with sockets for receiving the stump of the residual limb. Below the socket would be the shin portion with the foot below the shin. These wooden artificial limbs were covered with rawhide which often were painted. The sockets of most wood limbs were hollow, as the limbs were typically supported in the artificial limb by the circumferential tissue adjacent the stump rather than at the distal end of the stump. Some artificial limbs in Europe were also made from forged pieces of metal that were hollow. Fiber artificial limbs were also used which were stretched around a mold after which they were permitted to dry and cure. Again, these artificial limbs were hollow and pretty much supported the residual limb about the circumferential tissue adjacent the stump. Today, most artificial limbs are constructed from thermoplastics, such as polyester resins, acrylic resins, polypropylene and polyethylene, which are often laminated over a nylon stockinette that also may be impregnated by the various resins.
All of these various artificial limbs have sockets into which the amputee's stump is put. There are generally two categories of sockets. There are hard sockets wherein the stump is placed into the socket and actually touches the socket wall without any type of liner or stump sock. Another category of sockets is a socket that utilizes a liner or insert. Both categories of sockets typically were open ended sockets having a hollow chamber in the bottom and no portion of the socket touched the distal end of the stump. As a result, the stump was supported about its circumferential surface as it fit against the inside wall of the sockets
These types of sockets caused a lot of shear force on the stump, as well as had pressure or restriction problems on the nerve bundles and vascular flow of fluid by way of the circumferential pressure effect of the socket on the limb. This pressure effect could cause a swelling into the ends of the socket where an amputee may develop severe edema and draining nodules at the end of their stump.
With time, it was learned that by filling in the socket's hollow chamber and encouraging a more substantial contact between the stump and the socket, the swelling and edema problems could be eliminated. However, problematic tissue configurations, such as bony prominences, required special consideration, such as the addition of soft or pliable materials to be put into the socket.
In the past, most artificial limbs were suspended from the amputee's body by some form of pulley, belt or strap suspension, which was often used with various harnesses and perhaps leather lacers or lacings. Another method of suspending artificial limbs is known as the wedge suspension, wherein an actual wedge is built into the socket which is more closed at its top opening. The wedge in the socket cups a portion of the femur. Yet another form of suspension is referred to as the shuttle system, or a mechanical hookup or linkup, wherein a thin suction liner is donned over the stump that has a docking device on the distal end which mechanically links up with its cooperative part in the bottom of the socket chamber. Sleeve suspensions were also used wherein the amputee may use a latex rubber tube which forms into a rubber-like sleeve which would be rolled on over both the top of the artificial limb and onto the amputee's thigh. The sleeve suspensions have been used in combination with other forms of suspensions techniques.
Both the use of a positive pressure system and the use of a negative pressure system (or a hypobaric closed chamber or a vacuum) have been utilized in the field of prosthetics. At one time, for positive pressure systems “inflatable inner tubes” were used to fit into sockets. Presently, there are pneumatic “bags” which are strategically placed over what people consider to be good weight-bearing areas to increase pressure to help accommodate for volume changes within the socket.
Some of the problems with these positive pressure systems are that they use a very specific pressure at specific locations resulting in the creation of atrophy and loss of tissue dramatically over these high pressure areas. None of these systems employs positive pressure distributed over the total contact area between the residual limb and the artificial limb socket to accommodate volume changes within the socket.
One system using negative pressure utilized a closed chamber with a socket that is donned by pulling on with a sock, pulling the sock out of the socket and then closing the opening with a valve. This creates a seal at the bottom and the stump is held into the socket by the hypobaric seal.
The older systems were initially started in Germany. They were an open-ended socket, meaning there was an air chamber in the bottom of the socket. This did not work particularly well because it would cause swelling of the residual limb into the chamber created by the negative draw of suspending the weight of the leg and being in a confined area. This would lead to significant edema which would be severe enough to cause stump breakdown and drainage.
It was later discovered in the United States that total contact is important between the residual limb and the socket to reduce uneven force distribution. Once total contact is achieved, the weight was distributed evenly or the suspension was distributed over the whole surface of the limb rather than just over the open chamber portion of the socket.
The human body as a whole is under approximately one atmosphere of pressure at sea level. It keeps and maintains a normal fluid system throughout the body. When an amputee dons a prosthesis and begins taking the pressures of transmitting the weight of the body through the surface area of the residual limb to the bone, there is increased pressure on the residual limb equal to one atmosphere plus whatever additional pressures are created by weight bearing. This increased pressure causes the eventual loss of fluids within the residual limb to the larger portion of the body which is under less pressure. This loss of fluids causes the volume of the residual limb to decrease during the day. The amount of loss varies from amputee to amputee. The more “fleshy” and the softer the residual limb, the more volume fluctuation there will be. The greater the weight and the smaller the surface area, the greater the pressure will be and the more “swings” there will be in fluids. In the past, the amputee compensated for this volume decrease by removing the artificial limb and donning additional stump socks to make up for the decreased residual limb volume.
In order to achieve either positive or negative pressure within the socket, a pressure source of some type was needed. Numerous mechanisms and methods for providing and/or controlling pressure in the socket have been introduced over the years. For example, in U.S. Pat. No. 5,549,709, a hypobarically-controlled artificial limb for amputees is described as including, in part, an outer socket, a flexible, compressible inner socket within the outer socket with a cavity for receiving the residual limb and a vacuum source connected to the cavity. In U.S. Pat. No. 6,761,742, a weight-actuated vacuum pump and shock absorber for an artificial limb is described as including vacuum valves that connect a vacuum source to the inside of the socket. In FIG. 1, vacuum pump 120 is mounted beneath socket 102, in line with shin portion 104.
The connection of a pressure source to the interior of a socket has been accomplished using many techniques. One such technique involves providing a threaded metal elbow fitting to install in a socket, such as fitting 126 shown in FIG. 1. The technique was to drill an oversize hole, then fill the hole with epoxy resin/adhesive and allow the resin to cure. Then, a tap drill sized hole was drilled in the epoxy resin filling the hole, and the hole was then threaded with a tap. The purpose of filling the hole with epoxy was to provide a homogenous material to drill and tap. A homogenous material without filler or reinforcement tends to be less prone to air migration within the material. A typical definitive socket (the final socket intended to last a considerable period of time) will be made of a fiber reinforced resin. These materials have a tendency to delaminate when drilled and, if the material is porous, then air can migrate through the material to form a leak path. After metal elbow fitting 126 is attached to socket 102, flexible tubing 124 is used to connect elbow fitting 126 to valves 122 on vacuum pump 120.
The disadvantage of using a metal elbow fitting is that the fitting is very rigid, fairly large and protrudes from the side of the socket. If this fitting is bumped or jarred during the amputees daily activities, the stiff fitting transfers all of the impact load to the threads in the socket. The impact must then be withstood by the unreinforced epoxy material. This can result in breakage of the threads and subsequent pneumatic leaks.